Electric field effects on bacteria and yeast cells

Abstract

Comparative studies were carried out describing the lethal effects of electric pulses on GRAM-negative bacteria, GRAM-positive bacteria, and yeast cells. Microorganisms are killed by the pulse treatment without visible morphological destruction. The observed survival rates are figured as functions of the field strength E and the treatment time t (pulse number X time constant) revealing three explicit parameters as sufficient to explain the kinetics of the results. These parameters are determined by the species of microorganism used and moreover depend on the physiological properties of the microbial population. GRAM-positive bacteria and yeasts were found to be less sensitive to electric pulse treatment than GRAM-negative bacteria, when low pulse numbers are applied. Treatment with high pulse numbers reveals survival rates below 1% for all microorganisms examined. Cells from the logarithmic growth phase are killed in markedly higher percentage than cells harvested from the stationary growth phase. The obtained results as well as further studies confirm the hypothesis of an electric induced selective damage of inner cell membranes.

Effect of pulsed electric fields upon accumulation of magnesium in Saccharomyces cerevisiae

“…Further increase in the pulse width up to 125 ls had no statistically significant effect on the cell vitality; however, at the 150-ls pulse width, the culture contained already 35% necrotic cells. Hülsheger et al [27] reported over 99.99% inactivation of microorganisms exposed to peak electric fields of 20 kV/cm and pulses of several milliseconds.…”

“…The electric field can affect the cell membranes [21], which can irreversibly be damaged [22][23][24], influences the transport of ions [25] and structure of enzymes [26]. In a cell subjected to PEF-induced transmembrane tension facilitates the formation of pores in the membrane and leads to an increase in its permeability [27][28][29][30][31]. Electroporation temporarily eliminates integrity of the plasmatic membrane, i.e., produces small pores that close back with a time [31][32][33].…”

Influence of “Mild” Sonication Conditions on the Characteristics of <i>Streptococcus thermophilus</i> ST-M5

“…Liong and Shah [23] reported growth of Lactobacillus bulgaricus and Lactobacillus acidophilus to be predominant in the first 9 -15 h after which it reached a stationary phase. Simova et al [24] analyzed the growth characteristics of Streptococcus thermophilus T15 and L. bulgaricus HP1 by pre-incubating both cultures for 5.5 h before inoculation and reported that growth reached exponential phase in the first 5 h and stationary phase in 8 -12 h. Hülsheger et al [25] reported that the application of electric fields to E. coli cells increased their survival in the exponential phase of growth. In addition, Kobayashi et al [26] has demonstrated that low intensity of pulsed ultrasound treatments stimulates cell proliferation and production of proteoglycan in human nucleus pulposus cell line, possibly by enhancement of growth factor-related genes.…”

Moderate and high intensity pulsed electric fields : Effect on microbial inactivation, shelf life and quality of fruit juices

“…The efficacy of a high intensity PEF treatment strongly increases with increasing electric field strength (E) (Álvarez et al, 2003a;Heinz et al, 2002;Hülsheger, Potel & Niemann, 1981;Hülsheger, Potel & Niemann, 1983;. It is suggested that this increased efficacy only occurs, when the external applied electric field strength E exceeds the critical electric field strength (E c ) (Álvarez, Condón & Raso, 2006).…”

“…High intensity PEFs can inactivate vegetative bacterial cells, yeasts and moulds, although differences in sensitivity towards the PEF treatment are observed between microorganisms (Hülsheger, Potel & Niemann, 1983;Raso et al, 1998;Toepfl, Heinz & Knorr, 2007b). It has been suggested that the morphology of the micro-organism plays a role in its sensitivity to high intensity PEF treatment (Heinz et al, 2002).…”